Make writing Java code quick, fun, and productive with the Java Development Tools (JDT) in Eclipse. Explore all that the JDT has to offer you through a Java debug perspective, a Java project definition, editors, views, wizards, refactoring tools, and much more.

This chapter is from the book

This chapter is from the book

Eclipse provides a first-class set of Java Development Tools (JDT) for
developing Java code. These tools include a Java perspective, a Java debug
perspective, a Java project definition, editors, views, wizards, refactoring
tools, a Java builder (compiler), a scrapbook for evaluating Java expressions,
search tools, and many others that make writing Java code quick, fun, and
productive.

The JDT views and editors provide an efficient and effective way to quickly
and intuitively navigate through Java source code and view Javadoc. The Java
editor supports syntax highlighting, content assist, error cluing, state of the
art refactoring, type-ahead assistance, and code generation among a host of
other capabilities. The Java compiler is an incremental compiler; it compiles
only what it must based on your changes. It supports JDK 1.3 and 1.4. JDT can be
configured with different JREs. You can develop code with one JRE and debug with
another.

The Java editor is more than a source code editor. It builds and maintains
indexed information about your code, enabling you to quickly search for
references to classes, methods, and packages. The incremental compiler is
constantly running in the background and will alert you to potential errors in
your code before you save it. In many cases JDT will propose several solutions
to the problems it detects, such as adding an import statement that was
omitted, suggesting typographical corrections, or even creating a new class or
interface. This allows you to focus on your code and not be distracted by
compiler demands.

In the following sections we're going to look in more detail at the
capabilities and use of the Java tools. We'll start with an overview of the
JDT user interface and the fundamentals you'll need for creating and
navigating Java resources. We'll then look in much more detail at JDT
capabilities for coding Java. Then we'll see how to run Java code. In the
final sections of this chapter we'll get into more detail on working with
Java elements, tuning the performance of JDT, and specific functions in the JDT
views and perspectives.

Getting Started

Let's go. We'll start with a quick overview of the JDT user
interface. We'll then cover the fundamentals, like opening a class,
navigating to a method or field, and running a Java program. We'll also
discuss how to search Java code.

Overview of the JDT User Interface

The Java perspective is the default perspective for Java development and the
one that comes up when you create a new Java project (see Figure 3.1).

The left pane contains the Package Explorer view and Hierarchy view. The
Package Explorer view does for the Java perspective what the Navigator view does
for the Resource perspective. Use the Package Explorer view to navigate in your
Java projects, perform operations on resources, and open files for editing. The
middle pane contains open editors, Java and other- wise. The active editor is
the one on top. In Figure 3.1, an editor has PrimeNumberGenerator.java
open in it. The right pane is the Outline view, which presents a structured,
hierarchical view of the contents of the active editor. On the bottom right is
the Tasks view, the same one we saw in the section "Working with
Tasks" in Chapter 2. As you navigate in the user interface, selecting Java
files for editing and selecting Java elements, all the views and the editor stay
synchronized with your actions.

The Java views display Java elements with icons for a package and for
public methods. Some of these icons are decorated to provide further information
with overlays, such as to indicate a class has a main method or to indicate
a method overrides a method in a superclass. For a complete list of the JDT icons
and decorations, refer to the "Icons" section in the "Reference"
section in the Java Development User Guide.

You have two options for how code appears in the editor as you navigate in
the user interface. Show Source of Selected Element Only on the toolbar
controls this. The default is to show the contents of the entire file. If you
prefer to focus on smaller portions of code, toggling this option will only show
the source for the selected class, method, field, or import statement. This is
mostly a matter of personal preference.

The Fundamentals

Here are the fundamental tasks you need to understand to create and navigate
through Java resources. These are available when you are in one of the Java
perspectives.

Creating a Java Project

All
Java elements must exist in a Java project. To create a Java project, select
File > New > Project... > Java Project from the menu or select
Create a Java Project from the toolbar.

When creating Java projects and other elements, if you get the names wrong or
later decide you want to change them, the JDT refactoring capabilities make it
easy to rename elements and update references to them (refactoring will be
discussed in more detail later in this chapter).

Creating a Package

Java types, that is, classes and interfaces, must exist in a package. If you
do not create one, a default will be created for you. To create a package, select
the containing project and select File
> New > Package from the menu or select Create a Java Package
from the toolbar.

Creating a Type

To create a type, select the containing project or package and select File
> New > Class or File > New > Interface from the menu or
select Create a Java Class or Create a Java Interface from the
toolbar.

Opening a Type

To open a Java class or interface, do one of the following.

Double-click on a Java source file, class, or interface, or select one of
these in a view and press F3 or Enter. You can do this from any
Java view.

From the editor, select the name of a class or interface in the source
code (or simply position the insertion cursor in the name), and then select
Open Declaration from the context menu or press F3.

Select Ctrl+Shift+T and enter the name of a class or interface in
the Open Type dialog.

Opening a Method or Field

To open a method or field definition, do one of the following.

Double-click on a method or field, or select a method and press F3
or Enter to see its definition. You can do this from any Java
view.

From the editor, select the name of a method or field in the source code
(or simply position the insertion cursor in the name) and then select Open
Declaration from the context menu or press F3 to see its
definition.

Viewing Supertypes and Subtypes

To view the supertypes or subtypes for a class or interface in the Hierarchy
view, do one of the following.

Select a Java element, such as a Java source file, class, method, or
field, and then select Open Type Hierarchy from the context menu or press
F4. You can do this from any Java view.

From the editor, select the name of a Java element in the source code (or
simply position the insertion cursor in the name) and then select Open Type
Hierarchy from the context menu or press F4.

Select Ctrl+Shift+H and enter the name of a class or interface in
the Open Type in Hierarchy dialog.

Navigating to a Type, Method, or Field

You can navigate to class, interface, method, and field definitions in your
Java code simply by selecting one of these elements in a view, such as the
Outline or Type Hierarchy view. The editor and open views scroll to your
selection.

NOTE

If you select an element and you do not see it in an editor, it means the
file containing the definition is not open. You must then first open the file
using one of the methods described above.

Locating Elements in Projects

As you use the views and editor to navigate in your code, you can locate
element definitions in projects by selecting a Java element in one of the views
or the editor (or positioning the insertion cursor in the element name) and then
selecting Show in Package Explorer from the context menu. The Package
Explorer scrolls to the selected element. The element must be defined in an open
project in your workspace.

Running a Java Program

To run a Java program, select a class with a main method and then
select Run > Run As > Java Application from the menu. Output is
shown in the Console view.

Searching

There are two types of searches: a general Eclipse file search for text
strings, and a Java-specific search of your workspace for Java element
references. The search capability uses an index of Java code in your workspace
that is kept up-to-date in the background, independent of Java builds. This
means that you don't have to have the auto-build preference selected or
save your modifications in order to do a search.

Searching a File

To search the file in the active editor for any text, select Edit >
Find/Replace, or press Ctrl+F. Eclipse also has an "incremental
find" feature that provides a keystroke-efficient way to do this. Select
Edit > Incremental Find from the menu or press Ctrl+J and note
the prompt in the message area to the left on the bottom margin (see Figure
3.2). Start typing the text you're searching for. The message area displays
the text you're searching for and the first match is selected in the
editor. Press Ctrl+K to find the next occurrence of the text.

Searching Your Workspace

Select Search or press Ctrl+H and then select the Java
page to search your entire workspace, or a subset of it, for references to Java
elements. There are three aspects to a Java search: what kind of reference, what
kind of Java element, and within what scope. You can specify these by using
Limit To, Search For, and Scope, respectively, in the
Search dialog, as shown in Figure 3.3. To restrict a search, first select
one or more Java elements in the Package Explorer, Outline, or Type Hierarchy
view and then select Search, or define a Working Set and then specify
that working set under Scope. (For more information on Working Sets,
refer to the section "Working Sets" in Chapter 2.) For example, if you
want to search for methods returning void in your projects, select the
projects in the Package Explorer view, select Search, specify the
Search string "* void", select Search For
Method and Limit To Declarations, select Selected Resources,
and then select the Search button (or press Enter).

Java search results are shown in the Search view (see Figure 3.4). Matches
are indicated in the editor with entries on the marker bar. Navigate to matches
from the Search view by double-clicking an entry or by selecting Show Next
Match and Show Previous Match.

In all of the JDT views, including the Search view and the editor, you can
select an entry or Java element and then search on that element from the context
menu by selecting References > or Declarations >. This
ability to successively search for Java elements from the views, especially the
Type Hierarchy and Search views, provides a simple, efficient way to explore and
understand Java code.